# Why is it said that if we know few bits of pseudo random sequence we can predict the whole of it?

I am new to this cryptography and in the source from which i study it is said that if we know the first few bits of a pseudo random sequence we can predict the whole of it.How is it possible? The source:http://www.youtube.com/watch?v=NjedHm04ETM move to 7min 40sec and this is the source.

• That is not true out of context. Do you have the complete citation which says that? Jul 8, 2013 at 14:40
• You'll have to give more detail in your question for it to be answerable. What is the source? How is the pseudorandom sequence generated? In other words, we need more context to be able to answer your question. Jul 8, 2013 at 14:41
– rath
Jul 8, 2013 at 14:56

All psuedo random generators keep some limited state to calculate the next number in the sequence. you can think of it like a function $\delta(S)= \{output, S'\}$ with $S$ the internal state of the generator and represented by a finite number of bits.
As such if you get $n$ bytes of output with $n$ is larger than the number of bytes in the state then you can reasonably predict the current state of the output given enough time.